Design

1. Collector Orientation

Clean Energy Ireland recommends the collectors are orientated as much as possible to the
south. If there is no south facing aspect available then a westerly orientation should be used.

2. Collector Tilt Angle

The collector angle is often determined by the pitch of the roof, ideally the angle is in the
region of 45 degrees – 53 degrees to maximise year round sun heights. On-roof collector’s tilts can be varied by using special bracketing on pitched or flat roofs and also fitted on plinths.

3. Cylinder Size Requirements

For domestic solar systems typically the storage volume of the cylinder should be equal to 2 times the daily hot water demand.

To correctly size the storage volume the following formula should be used:

Vcyl = Minimum volume of cylinder (Ltr)
Vn = DHW demand per person/day (Ltr)
P = Number of people
Th = Temperature of hot water at outlet (°C)
Tc = Temperature of cold water
TDhw = Temperature of stored water

For example, a 3 person house with low demand:

= 216 litres. Therefore a 250 litre cylinder should be used.

4. Expansion Vessel Calculations

The correct sizing of the solar cylinder is important for a long life system. Clean Energy Ireland in association with Zilmet expansion vessel suppliers provides the following .xls format file to calculate the correct vessel sizes.

Expansion Vessel Calculator.xls (346 KB) >>

There is guidance provided in the field cells.

5. System Flow Rate

Clean Energy Ireland recommends a minimum flow rate of 1 litre/min/ m² of collector aperture area.

For example: 3 person household with 2 No. IDMK Integra Collectors ( aperture area = 2.32 m² per collector) and a 250 litre HWC, the system flow rate is:

System Flow Rate = 1.0 x 2 x 2.32 = 4.64 litres/min. ( = 4.64 x 60 = 278.4 litres/hour).

A Typical Solar Schematic with Auxiliary Heating.

6. Pipe Sizing

Ideally flow velocities in the pipe work should be between 0.4 and 1m/s, which should result in a pressure drop of between 1 and 2.5 mbar/m of pipe length.

The required internal diameter of the pipe work can be estimated using the equation: Φid =4.6√(Vs/v)
Where: Φid = Internal diameter of pipe (mm). Vs = system flow rate (litres/min). V = velocity of fluid (m/s).

For our example, with a system flow of 4.64 litres/min, take a fluid velocity of 0.5 m/s.

Then: Φid =4.6√(4.64/0.5) = 14.0mm

Therefore select a DN16 Solar metalflex stainless steel flexible pipe with a minimum internal diameter of 16.3mm.

7. PRV & Solar Discharge Vessel Sizing

The normal Clean Energy Ireland system pressure relief valve (PRV), manufactured by Watts Industriesis rated at 6 bar.

The Solar Discharge Vessel is sized to accommodate 1.5 times the total Solar Collector volume and must be capable of withstanding high temperature discharge.
For the example scenario being considered, the total Solar Collector volume
(from the expansion vessel spreadsheet) = 3.2 liters
Therefore the solar discharge vessel minimum volume = 1.5 x 3.2 = 4.8 liters.
Therefore a 5 litre solar discharge vessel is adequate.

8. Solar Pre-Installation Survey

The house and site needs to be suitable for the successful installation and effective operation of a solar system. This survey examines many aspects of an installation which when satisfied will lead to a successful installation and satisfied customer.

9. Legionnaires Prevention

The solar heating system should be designed so as to prevent the risks associated with bacterial growth, low water flow rates and scale formation whilst preventing risk of scalding due to high water temperatures. In order to reduce the risk of colonization of a water system the temperature of cold water in pipes and cisterns should not exceed 20C, and hot water should be stored and distributed at a temperature of not less than 60C with a temperature at the discharge point of 50C after one minute. Systems should be designed and operated to provide appropriate temperature control of water storage.

Information and guidance should be provided to the homeowner on the correct operation of these systems during normal operation and after periods of non use. For further guidance, refer to National Guidelines for the Control of Legionellosis in Ireland (HPSC, 2009) and The Management of Legionnaires’ Disease in Ireland (NDSC, 2002).

National Guidelines for the control of Legionella in Ireland (2,020 KB)  >>

Legionnaires Questionnaire

10. Planning Permission

The installation of solar panels up to 12m² aperture area, or 50% of total roof area, whichever is less, will be exempted subject to the following conditions:

• A 15cm maximum distance between the plane of a pitched roof and the solar panel
• A 50cm maximum distance between the plane of a flat roof and the solar panels, and
• That panels should be at least 50cm from the edge of the roof.

The exemptions provide for the same 12m² aperture areas in respect of free-standing arrays as applies to building mounted panels. Therefore, and as is the case with building mounted panels,arrays of this size and under are exempt from planning permission requirements, subject to some conditions.

These require that:

• Stand-alone panels must be no more than 2m in height,
• Such panels must be located behind the front wall of the house, and
• A minimum space of 25m² of useable space must remain for householders own private use.

11. Regulations & Standards

The solar water heating system should be installed in compliance with current building regulations, all local standards and health & safety regulations. These regulations are statutory documents and take priority over all the above recommendations.

For installation and operating procedures, please refer to the Installation and Operating manuals provided with the product.

For the Department of the Environment Technical Guidance documents please refer to the following website www.environ.ie